Magnetic pickup unit for musical instruments



Nov. 17, 1970 R. L. ABAIR MAGNETIC PICK UNIT FOR MUSICAL INSTRUMENTS Filed Oct. 15, 1968 INVENTOR. RAYMOND L. ABAIR ATTORNEY I United States Patent 3,541,219 MAGNETIC PICKUP UNIT FOR MUSICAL INSTRUMENTS Raymond L. Abair, Toledo, Ohio, assignor to Rowe Industries Incorporated, a corporation of Ohio Filed Oct. 15, 1968, Ser. No. 767,643 Int. Cl. Gh 3/00 US. Cl. 841.15 11 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an improved adjustable electromagnetic signal pickup unit for musical instruments, particularly stringed instruments, the pickup head including permanent magnets having a surrounding electrical coil employment to supply induced electrical signals corresponding to musical signals generated by the instrument with which the device is associated.

An object of the invention is to provide an improved high fidelity electromagnetic pickup unit for musical instruments in which distortion and reduction in output due to loading of surrounding conductive elements is minimized or practically eliminated.

Another object is to provide an adjustable electromagnetic pickup device of the character indicated in which surrounding electrically conductive magnet adjusting means is minimized as a distortion load in the fundamental and harmonic audible frequency range of the magnetic fields generated in the device.

A further object of the invention is to provide an enclosure and protective support for electromagnetic musical pickup devices which, although of conductive material in intimate proximity with the audio frequency magnetic field components of such devices, is practically eliminated as a distortion load on the signal circuits associated therewith.

A still further object of the invention is to provide an adjustable magnetic means which is rugged and capable of fine and positive setting with minimum possibility of deviation therefrom due to extraneous movement.

In brief, these objectives are attained according to the present invention by providing at least a thin transverse slit in electrically conductive loop elements in the pickup unit and particularly in the surrounding housing for the coil structure and in the conductive sleeves surrounding permanent magnetic pole pieces of such a unit.

A feature of the invention is its adaptability to provision of a more compact unit because circuit loading due to close proximity of surrounding electrically conductive components is practically eliminated.

Still further features of the invention lie in its ease of adaptability with a minimum of structural modification and its capability even to permit structural simplification while at the same time improving the fidelity of reproduction as well as electrical efficiency of the unit.

Other objects and features which are believed to be characteristic of my invention are set forth particularly in the appended claims. My invention, however, both in organization and the manner of construction, together with further objects and advantages thereof, may be best understood by reference to the following description taken in connection with the accompanying drawing in which:

FIG. 1 illustrates a stringed musical instrument utilizing a pickup unit of the present invention and showing the general arrangement of electrical amplifying equipment combined therewith for amplification of the output of the instrument;

FIG. 2 is an enlarged isometric view showing in greater detail the pickup unit in use on the instrument of FIG. 1;

FIG. 3 is a side elevational view of the pickup unit of FIG. 2;

FIG. 4 is a cross-sectional view of the unit taken on line 44 of FIG. 3;

FIG. 5 is a view of an adjustable permanent magnet pole piece of the pickup unit; and

FIG. 6 is a view of a threaded adjustment for a pole piece of the pickup unit.

Referring to the drawing in greater detail, FIG. 1 shows a guitar 10 having below its strings 20 in the vicinity of the instrument bridge an associated electromagnetic pickup device 11 which generates and supplies electrical signals corresponding to the string vibrations of the instrument. The signals are fed over the shielded conductor 12 to the control unit 14 and thence by way of a cord 15 to the amplifier unit 6 from which it is fed to the loudspeaker unit 17 for translation into audible mechanical vibrations.

The enlarged isometric view of the unit in FIG. 2 shows in greater detail the pickup 11 with its magnetic cores or pole pieces 21 each positioned in alignment below a diiferent string 20 of the guitar.

The housing 22 functions both to support and protect the electromagnetic coil assembly of the unit as well as to provide shielding for the pickup coil against extraneous radiation. The housing is open at the top with an inward flange overlying the top edge to define and bound an access region to the magnet core pieces, thereby to permit their vertical adjustable alignment into close proximity with the strings of the instrument. An outward extending flange at the base of the housing 22 provides means such as screw apertures for securement of the pickup assembly to the face of the stringed instrument. Accordingly the housing except as modified in accordance with the present invention is, in a sense, a frame-like configuration forming a continuous loop about the coil structure.

The coil 24 is wound on a base 23 made of a suitable nonmagnetic, insulating material such as cast nylon. As shown in FIGS. 3 and 4, the base is secured to the housing 22 such as by a suitable bonding adhesive 41 such as a thermosetting resin. Coil 24 is wound in a recess about the greatest perimeter dimension of the base and surrounds the central region through which the substantial permanent magnet cores 21 extend.

FIGS. 4, 5 and 6 show in greater detail the permanent magnet cores, each of which is provided with a surrounding sleeve 30 which is threaded on its exterior surface and fixedly mounted on the core by a suitable bonding material thereby permitting its being adjustably mounted in the coil base 23 as shown most clearly in FIG. 4. The thermosetting adhesive layer 41 holds the housing 22 and the coil base 23 in fixed bonded association. An aperture 40 extending vertically through the base 23 is provided for each of the magnetic cores 22, the aperture having a smaller more restricted dimension in its upper region to correspond closely to the diameter of the top portion of the permanent magnet core so that the core may extend loosely but closely through the aperture and project into the region of the opening of the cover 22. The bottom portion of the aperture 40 has a broader dimension than at the top and is threaded internally to accommodate in mated relationship the sleeve 30. Since as pointed out above, each sleeve 30 is fixedly bonded to its permanent magnet core 21 the magnet cores may be adjusted from the top of the pickup unit by providing a screwdriver slot at the top end of each thereby permitting the core to be moved up and down by screwdriver rotation of the sleeved core. Thus, when the pickup unit is mounted below the strings of a guitar as shown in FIG. 1, each of the magnet cores can be aligned vertically in proper relation with the respective strings of the guitar by rotational adjustment.

According to the present invention it has been found that when a slit 25 is provided in transverse relation across one side of the housing, the housing is prevented from acting as a short circuited loop and accordingly the housing oflers practically no electrical loading on the circuit associated with the electromagnetic coil enclosed therein.

A suitable coil 24 of the unit, for example, may be wound with 10,000 turns of #44 wire and can be made self resonant in the audible frequency range at about 7000 cycles. When the housing cover is continuous about the core as in prior art structures, it has been found that it acts as an electrical load on the coil and diminishes the amplitude of the output at resonance. This extra load causes the audio output to be what might be termed dead and mushy. By providing a transverse slit 25 or gap in the side of the housing as illustrated in FIGS. 2 and 3, this extra load and damping effect on the audible output is effectively removed.

It has also been found that sleeves of electrically conductive material on the pole pieces of the pickup unit affeet the fidelity of output and loading of magnetic Pickup circuitry. The pole pieces of the pickup are made up of highly magnetic material such as Alnico which is extremely hard and not readily threaded to permit adjustment within the coil structure. Accordingly threaded sleeve 30 of softer nonmagnetic material is placed upon one end of the magnet core. When these sleeves are of highly conductive material such as brass or aluminum, they act even more as a short circuit about the magnetic especially in view of their close proximity to the critical portion of the magnetic circuit.

In operation of units having continuous non-slit metal housings and metal pole sleeves, both the housing and sleeves generate secondary fields which oppose the main field of the unit and accordingly reduce the fidelity of output of the assembly. According to the present invention, each of the magnet sleeves 30 is provided with a transverse slit 31 extending from end to end through its side thereby breaking the continuity of the sleeve as a loop and preventing it from acting as a short circuit about the magnetic core. The amplitude and fidelity of the output of the pickup unit are therefore noticeably improved.

While the invention is herein described in relation to its use in pickup units for stringed instruments, it will be understood that the invention can be incorporated in other magnetic pickup units for musical instruments such as vibrating reed instruments as well as other instruments wherein base elements vibrate to produce musical responses. The pickup unit of this invention it will also be noted is practically reduced to its basic and essential components thereby assuring that extra conductive elements do not offer an electromagnetic load in the assembly and accordingly the assembly may be made much more compact, simple and correspondingly rugged in construction than has been the practice in the prior art. Thus, while the disclosure sets forth a particular form of the invention, it should be understood that it is intended that the invention not be limited specifically thereto, since many modifications may be made within the broad concepts of the invention, and it is therefore contemplated by the appended claims to cover all such modifications as fall within the true spirit and scope of the invention.

I claim: I

1. A magnetic pickup unit for musical instruments including a relatively hard substantially permanent elongate magnet, a cylindrical sleeve mounted in surrounding relation on said magnet and formed of nonmagnetizable metal, the external surface of said sleeve being provided with screw threads arranged to cooperate with a screw threaded non-metallic supporting base in said pickup and means operatively associated with said magnet whereby said sleeve and said magnet may be simultaneously adjusted, said sleeve having a transverse slit extending through its wall from end to end to make it an electrically noncontinuous path about said magnet.

2. A magnetic pickup according to claim 1, wherein said slit nonmagnetic sleeve is made of brass.

3. A magnetic pickup according to claim 1, wherein said slit nonmagnetic sleeve is made of aluminum.

4. A substantially permanent magnet and adjustably positioning assembly for stringed musical instruments, including a relatively hard metal substantially permanent magnet, a cylindrical sleeve of non-magnetizable metal, means between said magnet and sleeve to maintain said magnet and sleeve in fixed relative position, the external surface of said sleeve being provided with screw threads arranged to cooperate with a threaded non-metallic supporting core, whereby said magnet may be adjustably positioned relative to said core, said sleeve having a transverse slit through its wall to interrupt its continuity as an electrical loop.

5. A magnetic pickup unit for stringed musical instruments having an insulation portion forming a core, a coil wound on said core, an adjustable elongate permanent magnet extending from the top of said core into the region bounded by said coil, a frame-like housing surrounding the sides of said core and covering said coil, said housing having a tranverse gap therein extending from top to bottom to interrupt its continuity as an electrically conductive loop.

6. The magnetic pickup unit of claim 5 wherein the magnet has a nonmagnetic metal sleeve fixed thereon having screw threads on the outside thereof for coaction in threaded adjustable relation with said core, said sleeve having a transverse slit extending therethrough to also break its continuity as an electrically conductive loop.

7. A magnetic pickup unit for stringed musical instruments having a core body of insulation material, said core having a coil wound thereon, a plurality of separately adjustable elongate permanent magnets extending from the top face of said core into the region bounded by said coil, a frame-like housing surrounding the sides of said core over said coil and having an upper surface opening to provide adjustment access to said magnets, said unit being adapted to permit location of each of said magnets in aligned relation below a string of a musical instrument with which the unit is associated, said housing having a transverse slit extending from its top to its bottom to break its continuity as a complete electrical loop.

8. The magnetic pickup unit of claim 7 wherein the magnets are each provided with a metal sleeve fixed in surrounding relation therewith and having screw threads on the outside thereof for coaction in threaded adjustable relation with said core, said sleeves having a transverse slit extending therethrough to break its continuity as a complete electrical loop.

9. A magnetic pickup unit for stringed musical instruments having a core of insulation material, said core having a coil wound thereon, a plurality of separately adjustable elongate permanent magnets extending from the top face of said core into the region bounded by said coil, a frame-like housing secured to said core and surrounding the coil and sides of said core, said housing having an inturned flange overlying the upper edges of said core and bounding and defining an opening in its top to provide access for adjustment of said magnets, said housing having at its base an outward extending flange providing means for securement of the unit to a musical instrument, said housing having a transverse slit extending from its top to its bottom and through said flanges to interrupt its continuity as a complete electrical loop.

10. A magnetic pickup unit for stringed instruments having an insulation portion forming a core with a pcripheral recess therein, a coil wound in said recess, said core having a plurality of transverse openings extending from top to bottom of the core, a plurality of separately adjustable relatively permanent magnets, the transverse area of each of said openings being restricted for a distance below the top face of said core and having a broader threaded portion in its lower region, each said opening being in said core in a location for disposition below the string of an instrument, each of said transverse openings adapted to receive one of said adjustable magnets with the top end of the magnet accessible through the restricted area portion of its respective opening, each said magnet having attached thereto a nonmagnetic metal sleeve fixed in surrounding relation on a portion of its body and having screw threads on the outside of said sleeve to coact in rotationally adjustable threaded relation with the broader lower portion of its respective opening, each said sleeve having a transverse slit extending therethrough to break its continuity as an electrical loop.

11. The magnetic pickup of claim 10 wherein the core is provided with a metal frame housing cover secured thereto, an inturned flange around the upper edge of said housing adapted to fit around the edge of the upper face of said core, said inturned flange bounding and defining an opening in the top of said housing to provide adjustment access to the magnets in the respective restricted portions of each of said openings, said housing having a transverse slit extending therethrough extending from its top flange to its bottom to break its continuity as an electrical loop, thereby promoting the fidelity of reproduction of musical signals picked up by the unit.

References Cited UNITED STATES PATENTS 2,612,541 9/1952 De Armond 841.1S X 2,909,092 10/1959 De Armond et a1. 84-1.15 3,147,332 9/1964 Fender 841.15

HERMAN KARL SAALBACH, Primary Examiner S. CHATMON, J 11., Assistant Examiner US. Cl. X.R. 

